Horace Dediu and Dirk Schmidt analyze the sales numbers for Nintendo and Sony game consoles. The trend is bleak and clear:

The graphs above combine both Nintendo portable/consoles and Sony
portable/console sales. Note the similarity in patterns of growth.
It’s one thing to suggest that Nintendo consoles have “failed”,
it’s another to show that Nintendo consoles and portables have
failed, and yet another to show that two competitors in the games
business seem to be failing in unison across all their product
lines. The cyclicality is also over a long period of time: The
peak for the combined Sony/Nintendo was in 2008, five years ago.

No coincidence about the timing of that peak. It coincides with the beginning of the post-PC era.

The implications are that Nintendo, Sony and Microsoft are beyond
the point of no return in this industry. Gaming, as a business,
cannot be sustained as a platform independent of a general purpose
computer. Like other “applications” that used to have systems
built around them conforming to their needs the dedicated-purpose
solutions came to be absorbed into the general-purpose platforms.
And the modern general purpose computer is the smartphone.

My only quibble is with that last word, smartphone. Tablets are just as big a part of this trend. Better, I think, not to treat smartphones and tablets as separate categories, but merely as different sizes of the same thing.